Anyone driving west from Washington DC towards the Allegheny Mountains will arrive before long in a vast area without mobile phone signals. This is the National Radio Quiet Zone - 13,000 square miles (34,000 sq km) of radio silence. What is it for and how long will it survive?
As we drive into the Allegheny Mountains the car radio fades to static. I glance at my mobile phone but the signal has disappeared.
Ahead of us a dazzling white saucer looms above the wooded terrain of West Virginia, getting bigger and bigger with every mile. It's the planet's largest land-based movable object - the Robert C Byrd Green Bank Telescope (GBT) - 2.3 acres in surface area, and taller than the Statue of Liberty.
But it needs electrical peace and quiet to do its job.

The Quiet Zone, established in 1958, protects it from interference - and also the National Security Agency's main listening post at Sugar Grove nearby.
The GBT is highly sensitive and can detect radio waves emitted milliseconds after the birth of the universe. But when a signal has travelled so far, from so long ago, it can easily be drowned out.
"The telescope has the sensitivity equivalent to a billionth of a billionth of a millionth of a watt… the energy given off by a single snowflake hitting the ground," says business manager Mike Holstine. "Anything man-made would overwhelm that signal."
Hence the Quiet Zone, whose residents live a very different kind of life from most other Americans.
Not only are there no mobile phones, there are no baby monitors, microwave ovens or wireless doorbells.